ASCII
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ASCII (American Standard Code for Information Interchange) is a character encoding based on the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that work with text. Most modern character encodings, which support many more characters, have a historical basis in ASCII.
ASCII was created in 1963, was first published as a standard in 1967 and was last updated in 1986. It currently defines codes for 128 characters: 33 are non-printing, mostly control characters that affect how text is processed, and 95 are printable characters.
Like other character representation computer codes, ASCII specifies a correspondence between digital bit patterns and the symbols/glyphs of a written language, thus allowing digital devices to communicate with each other and to process, store, and communicate character-oriented information. The ASCII character encoding is used on nearly all common computers, especially personal computers and workstations. The preferred MIME name for this encoding is "US-ASCII".
ASCII is a seven-bit code, meaning that it uses the bit patterns representable with seven binary digits (a range of 0 to 127 decimal) to represent character information. At the time ASCII was introduced, many computers dealt with eight-bit groups (bytes or octets) as the smallest unit of information; the eighth bit was commonly used as a parity bit for error checking on communication lines or other device-specific functions. Machines which did not use parity typically set the eighth bit to zero, though some systems such as Prime machines running PRIMOS set the eighth bit of ASCII characters to one.
ASCII only defines a relationship between specific characters and bit sequences. Aside from reserving a few control codes for line-oriented formatting, it does not define any mechanism for describing the structure or appearance of text within a document. Such concepts are within the realm of other systems such as the markup languages.
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